This deck is pretty straight forward. 19 counterspells is enough to prevent boss's from doing A LOT of their powerful abilities, but the deck isn't literally just counters and resources. So there's more than just passing and countering for the mage player...The mage also geets to DPS via allies, and prevent the boss from attacking. The HERO POWER is amazing and used almost every raid on whatever the AoE encounter is.
I know I added 'Baxtan' who is horde, but I don't care. I never saw another time to play that card, and the synergy is fun.
By keeping card's cheap, you can usually always keep up counter magic, and keep refueling your hand with Corki's Ransom.

The 1-of's give the player some outs they wouldn't have otherwise.

By the way, don't try using all star counter card 'The Taste of the Arcana' it's only good vs PLAYERS, bosses always have lots of resources.